Semiconductor devices used in a power electronics field include MOSFETs (Metal-Oxide Semiconductor Field Effect Transistor) which are metal/insulator/semiconductor junction field effect transistor and IGBTs (Insulated Gate Bipolar Transistor), for example, and high reliability is required for the semiconductor device from a standpoint of an application to the power electronics.
For example, when, in a state where the MOSFET is applied to an inverter circuit to operate a dielectric load or a resistance load, a load short-circuit such as an arm short-circuit occurs and a high voltage which is a power-supply voltage is applied to a drain electrode of the MOSFET in an on-state, a large current flows through the MOSFET. In the above state, a drain current which is several times to tens of times as large as a rated current is induced on the MOSFET, and it leads to a breakdown of a MOSFET element unless the MOSFET has an appropriate protective function.
To prevent the above problem, there is a method that an excessive drain current (overcurrent) is detected prior to an occurrence of the element breakdown and an off signal is input to a gate electrode in accordance with the detection, so that the drain current is blocked. In the above case, robustness is required for the MOSFET element so that the occurrence of the element breakdown is prevented at least over a period of time from when the load short-circuit, for example, occurs and the overcurrent is detected until when the off signal is input to the gate electrode. That is to say, an excellent short-circuit resistance is strongly desired as one of the high reliability in the semiconductor device. The short-circuit resistance is substantially defined by an amount of time between the generation of the short-circuit and the element breakdown, and the excellent short-circuit resistance indicates that it takes a long time before the element breakdown.
Patent Document 1 discloses a technique of enhancing a short-circuit resistance of a MOSFET. The MOSFET of the Patent Document 1 has a configuration that a source region includes a low-resistance region (a source contact region and a source extension region) and a high-resistance region (a source, resistance control region). According to the above configuration, a voltage drop caused by a current flowing in the source resistance control region becomes large then load short-circuit occurs and a saturation current value decreases, so that the short-circuit resistance of the MOSFET is enhanced.